A German Sparpreis-ticket is (for long-distance trains) only valid on the trains indicated on the ticket, but a seat reservation is optional. In case of overcrowding, a Sparpreis ticket holder can be denied boarding to the indicated train. What rights to alternate transportation or restitution does the traveller have in this case, assuming domestic travel?
Based on common sense and consumer protection, I would expect that if Deutsche Bahn cannot deliver what the traveller paid for, then either the ticket should be valid on a later train or should be reimbursed. Therefore, I find the accepted answer on community.bahn.de (which states the opposite)¹ hard to believe.
What are my rights if I am (to no fault of my own) denied boarding to the train indicated on my ticket?
¹ Relevant part from linked page:
Nein die Zugbindung ist nicht aufgehoben und daher muss ich der Aussage von Euklid93 widersprechen. Nutzen Sie einen anderen Zug so zahlen Sie einen komplett neuen Fahrschein.
No, the train linking is not lifted and therefore I must contradict the statement by Euklid93. If you use another train then you will pay a complete new ticket.